Process for removing hydrogen fluoride from a gaseous mixture containing hydrogen fluoride and hydrogen chloride



United States Patent 3,353,911- PROCESS FOR REMOVING HYDROGEN FLUO- 'RIDE'FROM A GASEOUS MIXTURE CONTAIN- ABSTRACT OF THE DISCLOSURE Gaseous hydrogen fluoride is removed from gas mixtures containing hydrogen fluoride and hydrogen chloride by bringing the gases into contact With an aqueous absorbent solution of boric acid saturated with hydrogen chloride from the gaseous mixture.

3,353,911 Patented Nov. 21, 1957 through a suitable gas liquid contacting device, such as a packed tower irrigated with an aqueous solution of boric acid in hydrochloric acid.

' With such an aqueous boric acid solution containing 510% w./w. 'HF with a fluorinezboron atomic ratio of between 2:1 and 4: 1, and saturated with HCl at a partial I pressure of ca. 0.5 atrn., it is possible to reduce the HF content of HF/HCI gas mixtures to the equivalent of 0.01% w./w. HP in w./vv. hydrochloric acid.

The range of F:B atomic ratios permissible in the boric acid solution; is determined by the following considera-' tions. The upper limit of 4:1 obviously cannot be exceeded since the mechanism of the removal reaction:

Results obtained from runs carried out on HF and HCl containing gas mixtures are tabulated below:

Absorber solution, HiBOaIHFIHCI Gas Composition, Mole ratio, HC1:HF Original, percent w./w. Mole ratio Final, percent w./w. by analysis HF 3130:: F:B HF H3130; H01 Inlet Outlet 1. 68 2. 64 2. 0:1 2.05 2. 49 36. 3 36:1 1, 839:1 5.0 7.98 1.9:1 5.2 7.4 33.0 30:1 8, 70011 5.0 4.46 3.5:1 5.3 4.8 33.7 36:1 4, 770:1 7.5 7.75 3.0:1 7.4 7.1 32.3 32:1 4,35011 7.5 10.4 22:1 7.5 9.5 31.3 62:1 4,900zl 10.0 10. 4 3. 0:1 9. 6 l). 5 29. 8 145:1 6, 400: 1 10.0 15.0 2.1:1 9. 7 13.9 28.0 81:1 1, 600:1 7.5 6. 3.5:1 6.8 6.2 32.8 :1 3, 310:1 10. 0 9. 76 3. 2:1 9. 7 8. 8 30. 5 92: 1 3, 1 15.0 11. 8 3. 9: 1 14. 2 10. 6 26. 0 46:1 1, 590: 1

This application is a continuation-in-part of our pendingapplication Ser. No. 418,860, filed Dec. 16, 1964, for improvements in or relating to the Separation of Hydrogen Fluoride and Hydrogen Chloride Mixtures (since abandoned).

This invention relates to a method of removing gaseous hydrogen fluoride from gas mixtures containing hydrogen fluoride and hydrogen chloride.

Prior art It is known that hydrogen fluoride can be removed from hydrogen chloride gases by' first passing the gases through a glass wool or other siliceous material to com vert the HF into SiF and then contacting the SiF, with solid boric acid. Very nearly complete removal of HP from the gases is claimed.

Brief summary of the invention From these results it can be seen that the absorption of HP in the H BO can be continued until the molal F:B ratiohas risen nearly to 4 (corresponding to the composition of HBF As is well known, commercial boric acid, indicated generally at H BO is not pure. Other boric acids may be present, also produced from boric oxide, B 0 with varying amounts of water. See 2 Encyclopedia of Chemical Technology 602 (1948). This is true also of fluoboric acid, indicated generally as HBF and often called tetra fluoboric acid or borofluoric acid. Other fluoboric acids may be present, also produced by dissolving boric acid in hydrofluoric acid, usually indicated by such reactions as:

See 6 Encyclopedia of Chemical Technology 684-6 (1951). In other words, other fluoboric acids, such as HBF (OH) and HBF (OH are known and may be present; the so-called fluoboric acid is not necessarily present solely as pure HBF It is our understanding (1) that the reaction between H BO and HF proceeds by stages, e.g.

(2) that the existence of HBF (OH) and HBF (OH) has been confirmed; but (3) that the existence of 3 HBF(OH) is purely speculative; and that it is therefore to be expected that the solution of HF, H BO and HCl will contain a mixture of fluoboric and hydroxyfluoboric acids, boric acid and hydrochloric acid.

Various modifications may be made within the scope of the invention.

What we claim is:

1. In the method of removing gaseous hydrogen fluoride from a gaseous mixture containing hydrogen chloride and hydrogen fluoride, the improvement which comprises bringing a mixture of the gases containing a major proportion of hydrogen chloride and a minor proportion of hydrogen fluoride into intimate contact with an aqueousabsorbent solution of boric acid, said boric acid solution being saturated with hydrogen chloride from the gaseous mixture to inhibit absorption of hydrogen chloride from the gaseous mixture, and maintaining the partial pressure of the hydrogen chloride in the boric acid solution equal to the partial pressure of the hydrogen chloride in the gaseous mixture to facilitate absorption of the hydrogen fluoride from the gaseous mixture into the boric acid solution to form an aqueous solution of fluoboric acid.

2. Method according to claim 1, in which the aqueous boric acid absorbing solution contains a fluorine to boron atomic ratio of between 2: 1 and 4: 1.

3. Method according to claim 1, in which the aqueous boric acid absorbing solution contains a fluorine to boron atomic ratio of between 2:1 and 4:1, and is saturated I with HCl at a partial pressure of about 0.5 atm.

References Cited UNITED STATES PATENTS OSCAR R. VERTIZ, Primary Examiner. E; STERN, Assistant Examiner UNITED STATES PATENT OFFICE CERTIFICATE OF CORRECTION Patent NC). November Leopold M01161 et al.

It is certified that error appears in the above identified patent and that said Letters Patent are hereby corrected as shown below:

Columns 1 and 2, in the table, eight column, line 8 thereof,

for "81 '1" read 82 '1 same table ninth col ggirigf f0rd"4,831:1" read 4,830:1 column li r l I 9 rea as llne 54, for "HBF read HBF OH Signed and sealed this 22nd day of July 1969.

(SEAL) Attest:

WILLIAM E. SCHUYLER, JR.

Commissioner of Patents Edward M. Fletcher, Jr.

Attesting Officer 

1. IN THE METHOD OF REMOVING GASEOUS HYDROGEN FLUORIDE FROM A GASEOUS MIXTURE CONTAINING HYDROGEN CHLORIDE AND HYDROGEN FLUORIDE, THE IMPORVEMENT WHICH COMPRISES BRINGING A MIXTURE OF THE GASES CONTAINING A MJAOR PROPORTION OF HYDROGEN CHLORIDE AND A MINOR PROPORTION OF HYDROGEN FLUORIDE INTO INTIMATE CONTACT WITH AN AQUEOUS ABSORBENT SOLUTION OF BORIC ACID, SAID BORIC ACID SOLUTION BEING SATURATED WITH HYDROGEN CHLORIDE FROM THE GASEOUS MIXTURE TO INHIBIT ABSORPTION OF HYDROGEN CHLORIDE FROM THE GASEOUS MIXTURE, AND MAINTAINING THE PARTIAL PRESSURE OF THE HYDROGEN CHLORIDE IN THE BORIC ACID SOLUTION EQUAL TO THE PARTIAL PRESSURE OF THE HYDROGEN CHLORIDE IN THE GASEOUS MIXTURE TO FACILITATE ABSORPTION OF THE HYDROGEN FLUORIDE FROM THE GASEOUS MIXTURE INTO THE BORIC ACID SOLUTION TO FORM A AQUEOUS SOLUTION OF FLUROBORIC ACID. 